1. Field of the Invention
The present invention relates to a microsurgical apparatus and, more particularly, a noncontact laser microsurgical apparatus adapted for use in cornea transplant surgery, keratoplasty, keratotomy, and other corneal surgery techniques.
2. Description of the Related Art
Despite advances in corneal preservation and transplantation techniques, postoperative astigmatism remains the most important complication limiting visual acuity after a corneal transplantation.
In order to reduce such postoperative astigmatism, U.S. patent application Ser. No. 07/056,711 filed Jun. 2, 1987 entitled "A Cornea Laser-Cutting Apparatus", assigned to the same assignee as the present application, discloses that trephination of either a donor cornea or a recipient cornea may be performed utilizing a laser cutting technique.
During penetrating keratoplasty, it is further necessary for a surgeon to align the circumferences of the donor corneal button and recipient cornea. To this end, there have been recently developed mechanical marking apparatuses such as those described in Pflugfelder et al. "A Suction Trephine Block for Marking Donor Corneal buttons," Arch. Ophthalmol., Vol. 106, Feb. 1988, and Gilbard et al. "A New Donor Cornea Marker and Punch for Penetrating Keratoplasty," Ophthalmic Surgery, Vol. 18, No. 12, Dec. 1987.
However, such mechanical marking apparatuses directly contact and distort the cornea such that the marking process is not always precisely accomplished and sometimes results in post-keratoplasty astigmatism.
In radial keratotomy, mechanical contact type surgical utensils as shown in U.S. Pat. No. 4,417,579 have been used to radially incise the cornea of a patient's eye. This surgical method is apt to cause strain and/or deformation of the cornea, and also results in postoperative astigmatism.
Noncontact microsurgery of the cornea would minimize distortion of the cornea tissue, as occurs in contact-type techniques, and would decrease the likelihood of producing postoperative astigmatism. The use of lasers provides the potential for such noncontact microsurgery.
Excimer lasers have been investigated in the past to produce linear corneal incisions or excisions. The argon fluoride excimer laser emitting at 193 nm has been shown to produce sharp, smooth-walled corneal cuts. More recently, the hydrogen fluoride, Q-switched Er:YAG, and Raman-shifted Nd:YAG lasers emitting at about 2.9 um (micro meters), which corresponds to the peak absorption wavelength of water, have been experimentally used to produce linear corneal incisions or excisions.
Industrial laser cutting by focusing the beam into a ring has been proposed as a method for drilling large diameter holes. The axicon, a diverging prismatic lens, has been used for such industrial purposes. An axicon system has been used by Beckman & Associates to study corneal trephination with a carbon dioxide laser. This experimentation is described in an article entitled "Limbectomies, Keratectomies and Kerastomies Performed With a Rapid-Pulsed Carbon Dioxide Laser," American Journal of Ophthalmology, Vol. 71, No. 6, (Jun. 1971). In this article, Beckman et al. describe the use of an axicon lens in combination with a focusing lens to form an "optical trephine" and perform various corneal experiments with animal's. The diameter of the trephine was governed by the focal length of the focusing lens in these experiments. Therefore, to vary the diameter of the annular beam it was necessary to change the focusing lens which acted to change the width of the annular ring and, thus, varied the amount of tissue incised or excised by the laser. Moreover, changing the focusing lens requires a time consuming process for each patient or donor. In addition, the optical system proposed in the Beckman et al. article requires the use of multiple focusing lenses of different focal length.
Accordingly, it is an object of the present invention to provide a noncontact laser microsurgical apparatus and method of using the same which substantially eliminates strain and/or deformation on a cornea during and after trephination.
Yet another object of the present invention is to provide a noncontact laser microsurgical apparatus and surgical method which is capable of marking a recipient cornea and a donor corneal button with a suture track during keratoplasty, and which incises or excises selected portions of a cornea radially and/or paraxially during keratotomy.
Still another object of the present invention is to provide a noncontact laser microsurgical apparatus and surgical method which is capable of performing thermokeratoplasty for curing corneal refractive error and/or astigmatism of a patient's eye.
It is still another object of the present invention to provide a noncontact laser microsurgical apparatus and method capable of surgically "welding" donor tissue or synthetic material and recipient corneal tissue together thereby eliminating the necessity of suturing the donor and recipient parts to one another in penetrating and epikeratoplasty procedures.
It is still a further object of the present invention to provide a noncontact laser microsurgical apparatus and method wherein selected areas of the cornea may be caused to shrink so as to change the curvature of the natural lens thereby curing or alleviating corneal refractive error and/or asigmatism.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.